Switch-mode power supplies (SMPSs) (“power converters”) are widely utilized in consumer, industrial and medical applications to provide well-regulated power while maintaining high power processing efficiency, tight-output voltage regulation, and reduced conducted and radiated electromagnetic interference (EMI).
To meet these conflicting goals, state-of-the-art power converters (fly-back converters, forward converters, boost converters, buck converters, and so on) commonly utilize quasi-resonant control methods. Quasi-resonant control methods induce a resonant waveform having sinusoidal voltage oscillations at the drains of one or more semiconductor switches of the power converter. Through well-timed control actions, the semiconductor switches are turned on at the instants where the drain voltage is minimum (i.e., valley switching), thus minimizing the semiconductor switching losses and drain-source dv/dt slope, leading to increased power processing efficiency and reduced electromagnetic interference (EMI).
To maintain these benefits across an entire operating range of the power converter, it is often necessary to “hop” between the valleys of the resonant waveform in such a way as to minimize the sum of the conduction and switching losses (which are generally inversely proportional to each other). However, during the valley hop transitions, output voltage disturbances are introduced. Furthermore, if there are frequent and/or repeated low-frequency mode transitions, audible noise may be generated by the magnetic and/or capacitive elements of the power converter.
Typically, this issue is partially addressed by introducing large valley hopping hysteresis constraints. However, such methods negatively affect power processing efficiency and eliminate any potential spread-spectrum benefits from more frequent valley hopping. In addition, a large output voltage disturbance is still introduced as a result of such valley mode transitions.